This immediately presents Plantinga with an apparent problem. Plantinga wants to claim that Aquinas and other Natural Theologians subscribe to the Evidentialist Credo. But Aquinas explicitly maintains that there is a central role for faith in theism. Given that, how can we say that he believes the Credo? To see the answer to this, Plantinga thinks we need to take a close look at Aquinas’ discussion of faith, and the contrast he draws with knowledge.
Aquinas on Knowledge and Faith
For Aquinas, knowledge is a product of “demonstration”. What we can know, for Aquinas is what we can “demonstrate”. By “demonstration” Aquinas means deduction from propositions that are all self-evident or evident-to-the-senses.Aquinas holds that there are certain theistic propositions that can be demonstrated, and thus that we “know” in his strong sense of the term. Examples include the propositions “God exists”, “God is good”, and “God created the world”. There are demonstrations that start with self-evident premises and lead to these theistic conclusions. His “Five Ways” are just such demonstrations (the Causal Cosmological Argument is one of these ways of proving the existence of God).
So, for some theistic propositions and some people, faith is not necessary. Such people can know that, e.g., God exists because they can carry out the required demonstrations. However, for most people these demonstrations are too hard, or too time consuming, to follow successfully. For most people then, these theistic propositions must be believed on faith.
Further, Aquinas thinks that there are other theistic propositions which cannot be demonstrated by anyone, e.g. “God is Triune”. Thus, everyone must believe such propositions merely on faith.
So, for Aquinas faith enters the picture in two different places. Most people’s religious beliefs are entirely based on faith. For some people this isn’t the case. Some people are able to “know” certain religious propositions. But even for these intelligent people with plenty of time on their hands, many of their religious beliefs are still based on faith.
"Believing on Faith"
Thus far, we’ve only seen Aquinas’ definition of knowledge. That definition, along with some additional claims, shows that Aquinas needs to allow a large role for faith in religious belief. But we still haven’t seen what Aquinas’ account of faith is.Before looking directly at his definition, it’s worth reminding ourselves of why the issue is important to Plantinga. Remember, Plantinga wants to claim that Aquinas is committed to the Evidentialist Credo. But we’ve just seen that faith plays a substantial role in Aquinas’ picture of religious belief.
So, the pressing question is whether Aquinas holds that “believing on faith” is believing in the absence of evidence. If Aquinas does hold that faith involves a lack of evidence, this would go against the Evidentialist Credo.
And the main point that Plantinga wants to make is that this is not the case for Aquinas. For Aquinas, to “believe on faith” is not to believe in the absence of evidence, nor is it to believe on the basis of feelings. As Plantinga puts it:
“Fundamentally, for Aquinas, to accept a proposition on faith is to accept it on God’s authority; faith is a matter of ‘believing God’.” (63)Now that may sound paradoxical, but Plantinga argues that it isn’t. It is perfectly reasonable to believe something on another person’s authority: e.g. you may believe that Fermat’s Last Theorem has been proved because your math teacher tells you so. (This is a good example, since we can suppose that you personally couldn’t understand the proof yourself.) So, as Plantinga writes:
“the question is not whether it is foolish to believe something on God’s authority, but whether it is foolish to believe that God has in fact proposed a given item for my belief.” (64)And (here’s the punch-line) with respect to those propositions that cannot be demonstrated (and presumably for the ones that can as well) we have evidence for the conclusion that God has proposed them for our belief (“revealed” them to us). For instance, the fulfillment of prophecy, miracles like the curing of illness, the raising of the dead, etc. all provide evidence for the conclusion that the Scriptures are the true revealed word of God. And so since the Scriptures teach, e.g. that God is triune, we have reason to believe these sorts of propositions.
So, in the end, Aquinas’ view is that both “knowledge” and “faith” rest on a certain kind of evidence:
This is why Plantinga claims that Aquinas’ view is committed to the Evidentialist Credo. (Further, given the kind of evidence that Aquinas thinks beliefs must rest on, Plantinga claims that Aquinas is committed to Classical Foundationalism.)
